Mammalian reproduction conventionally requires oocytes provided by a female and sperm provided by a male to achieve fertilization. We go beyond this convention and propose the hypothesis that an adult individual of any sex can be induced to produce gametes of the opposite sex, and that these gametes are functional in assisted fertilization. The premise for this hypothesis comes from our recently published studies demonstrating that genetically engineered male mice with limited or no Y chromosome genes can successfully reproduce by assisted fertilization (ART), and from significant advancements in field of cell reprogramming and differentiation. Our laboratory has shown that in the mouse only two Y chromosome genes, testis determinant Sry and spermatogenesis driver Eif2s3y, are sufficient for a male to produce haploid male gametes functional in ART. We have subsequently demonstrated that the function of these two genes could be replaced by that of their homologues encoded on other chromosomes, and that a mouse with a single X chromosome (XO) lacking all Y chromosome genes can produce male gametes and sire healthy offspring after assisted fertilization. The laboratory of our collaborator, Mitinori Saitou, has shown that both male and female gametes can be obtained from induced pluripotent stem cells (iPSC) differentiated into primordial germ cell like-cells (PGCLC). In this proposal, we marry our findings and expertise and ask 3 questions: Aim 1. Can an adult female mouse produce male gametes functional in assisted fertilization? Aim 2. Can an adult male mouse produce female gametes functional in assisted fertilization? Aim 3. Can an adult mouse of either sex sire uniparental offspring? To address these questions we will develop somatic cell lines from an adult mouse of a given sex, reprogram to iPSC, identify the clones that have lost one sex chromosome and became XO, and differentiate into PGCLC. To produce male gametes we will transgenically add a spermatogenesis driver and transplant PGCLC to testes from neonatal males. To produce female gametes we will reconstitute ovaries in vitro and transplant them under ovarian bursa of recipient females. We will test the function of such derived male and female gametes using assisted reproduction. To produce uniparental offspring, male and female gametes derived from the same individual will be used for fertilization. The findings from this project will impact on our understanding of sex specific differences, especially pertaining to effects of sex chromosomes and X and Y genes on germline development. If successful, we will also provide the field with a proof-of-principle that offspring of both sexes can be obtained from a single individual, which will impact on species preservation.